Blue beam correcting devices for color television receiving tubes



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INVENTORS EIJ I SAWADA BY HIROSHI IKEUCHI United States Patent O 3 533 031 BLUE BEAM CORRECTING DEVICES FOR COLOR TELEVISION RECEIVING TUBES Eiji Sawada, Tokyo, and Hiroshi Ikeuchi, Yokohama,

Japan, assignors to Denki Onkyo Co., Ltd., Tokyo, Japan, a corporation of Japan Filed July 1, 1968, Ser. No. 741,611 Claims priority, application Japan, July 5, 1967, 42/57,928 Int. Cl. H01f 1/00 US. Cl. 335212 4 Claims ABSTRACT OF THE DISCLOSURE BACKGROUND OF THE INVENTION This invention relates to a magnetic beam control device more particularly to a blue electron beam correcting device wherein the blue beam of a color television receiving tube is corrected and shifted to concentrate red, blue and green electron beams onto a set of fluorescent trio at the center of the screen.

In three electron gun type color television receivers, in case where three electron beams do not concentrate onto a set of fluorescent trio at the center of the screen due to manufacturing tolerance and the like of the receiving tubes it is usual to adjust thru electron beams by applying a DC field thereto by means of a static convergent, permanent magnet means.

However, there are some cases wherein it is impossible to concentrate three electron beams at the center of th screen even with the maximum adjustment of the DC magnetic field. More specifically, even when the red beam and green beam are caused to concentrate at the center of the screen by the adjustment of the permanent magnet, in some cases it is impossible to bring the blue beam to the point of concentration of red and green beams by the vertical adjustment of the blue beam. In such a case a correcting device or a so-called blue lateral device is utilized by means of which a DC magnetic field is applied to the blue beam in the vertical direction whereby to shift it in the lateral direction.

According to a prior arrangement a pair of permanent magnets symmetrically disposed with respect to the axis of a receiving tube are brought to and from a neck of the tube to vary the intensity of the DC field acting upon three electron beams. However, owing to the limited space around the neck and the physical dimension of the adjusting device it is desirable to make zero the DC field acting upon three electron beams at a definite distance from the neck of the reeciving tube or at a point near the limit of movement of the permanent magnets. One approach to this problem proposed by the applicant involves the provision of a metal piece of high permeability at a point near the limit of the movement of the permanent magnets so that when permanent magnets are moved away from the neck and reach said limit of movement the magnetic fiux established by the permanent magnets also flows through the metal piece.

Such construction, however, requires a special configuration of the metal piece or magnetic short circuiting Patented Oct. 6, 1970 ice member in order to make perfectly zero the DC field at the limit of movement.

SUMMARY OF THE INVENTION Accordingly, it is an object of this invention to provide an improved blue beam correcting device for a color television receiving tube which can reduce substantially to zero the DC field provided by permanent magnets at their limit of movement.

Another object of this invention is to increase the variation of the DC field in a limited space.

A further object of this invention is to provide a correcting device of simple construction and of cheap price.

According to this invention, in the blue beam correcting device of the type described, E-shaped magnetic members are provided at the limit of movements of the magnets to magnetically short circuit these magnets so as to completely divert the magnetic flux from the neck.

BRIEF DESCRIPTION OF THE DRAWING Further objects and advantages of the present invention will become apparent and this invention will be better understood from the following description taken in connection with the accompanying drawing in which:

FIG. 1 is a diagrammatic plan view partly in section, of a typical blue beam correcting device for a color television receiving tube;

FIG. 2 is a simplified plan view helpful to explain the principle of the novel blue beam correcting device;

FIG. 3 is an enlarged front view of a portion of one embodiment of the blue beam correcting device;

FIG. 4 is a sectional view along a line IV-IV in FIG. 3 and viewed in the direction of arrows;

FIG. 5 is an enlarged perspective view of one example of a magnetic bridging member; and

FIG. 6 is an enlarged perspective view of one example of an elevating member including a pair of permanent magnets.

DESCRIPTION OF THE PREFERRED EMBODIMENTS Referring now to the accompanying drawing, FIG. 1 is a view to explain the operation of a typical blue beam correcting device of a color television receiving tube. As shown in this figure, a neck 11 of a receiving tube is mounted in an inner frame 13 disposed eccentrically with respect to an outer frame 12. The outer frame 12 is disposed within a cylinder 14 to be rotatable therein, said cylinder 14 being provided with elevating frames 15 and 16 which are spaced apart around the periphery of the cylinder 14. Side walls of elevating frames 15 and 16 are formed with grooves 19, best seen in FIG. 4, to guide elevating members along the frames 15 and 16. Each one of elevating members 17 and 18 carry a pair of oppositely inclined permanent magnets 23, 24 and 25-, 26. These magnets are properly secured to elevating members with their poles of the same polarity opposing each other. Thus, for example, N poles of permanent magnets 23 and 24 secured to elevating member 17 face each other whereas S poles of permanent magnets 25 and 26 secured to elevating member 18 face each other. A rotatable circular disc 27 is mounted closely adjacent the cylinder 14 carrying elevating frames 15 and 16. Disc 27 is provided with spiral grooves 28 and 29 to receive projections 30 and 31 of the elevating members 17 and 18- whereby as the disc 27 is rotated, elevating members 17 and 18 are caused to move along the elevating frames in the vertical direction. Consequently, when permanent magnets 23, 24, 25 and 26 are brought close to the tube neck 11 their DC field greatly influences upon the electron beams through neck 11 whereas as the magnets are moved away from the neck their influence is reduced.

Referring now to FIG. 2 which is useful to explain the principle of the blue beam correcting device of this invention, there are provided E-shaped magnetic bridging members 32 and 33 of a magnetic material which are positioned near the limit of movement of elevating members 17 and 18. Accordingly, when elevating members 17 and 18 reach their limit of movement respective permanent magnets would assume positions shown in FIG. 2 so that magnetic flux established by permanent magnets 23, 24, 25 and 26 will be completely shunted around or diverted away from the neck 11 by outer legs 34, 35, 37 and 38 and central legs 36 and 39 of the magnetic bridging members. In other words, permanent magnets 23, 24, 25 and 26 will be perfectly short circuited magnetically by magnetic bridging members 32 and 33 so that any appreciable fiux would not pass through the neck. Thus, when the elevating members 17 and 18 reach their limit of movement, the magnetic flux through neck 11 can be reduced to substantially zero.

FIGS. 3 to 6 illustrate practical constructions of the correcting device of this invention. FIGS. 3 and 4 illustrate a condition wherein elevating member 17 has reached its limit of movement. As mentioned hereinabove, the elevating member 17 is caused to slide along guide groove 19 on the side walls of elevating frame 15 by the rotary movement of disc 27.

FIG. 5 illustrates one example of the construction of magnetic bridging members 32 and 33, as shown it has generally a letter B shape, the length of outer legs 34, 35, 37 and 38 being longer than central legs. This is because the permanent magnets 23, 24, 25 and 26 are inclined. However it will be clear that these outer legs may have nearly equal length as center legs.

FIG. 6 illustrates one example of elevating members 17 and 18. The elevating member shown in FIG. 6 has a t central recess 41 and two sliding members 42 and 43 on both sides. Permanent magnets 23, 24 (or 25, 26) are secured to walls on both sides of the central recess 41 so that when elevating members 17 and 18 reach their limit of movement central legs 36 and 39 of the magnetic bridging members 32 and 33 will be received in recesses 41 of elevating members 17 and 18 while outer legs 34,

35 and 37, 38 will slide along sliding members 42 and 43. J

Although in this embodiment the magnetic bridging members are secured to the upper ends of the elevating frames they may be inserted in the elevating frames from the side thereof. The magnetic bridging members may be made of magnetic ceramics or iron, and when it is made of iron plates the plates may be suitably bent.

While the invention has been shown and described in terms of preferred embodiments thereof it should be understood that many alternations and modifications can be made within the scope of the invention as defined in the appended claims.

What is claimed is:

1. A blue beam correcting device for a color television receiving tube comprising a first pair of spaced apart magnets disposed at a first predetermined position on the outer periphery of the neck of said receiving tube, a second pair of spaced apart magnets disposed at a second predetermined position on the outer periphery of said neck diametrically opposite to said first pair, means to adjust in union said first and second pairs of magnets with respect to the axis of said tube neck, and magnetic bridging means including letter E shaped magnetic members positioned at the limit of movement of said magnet pairs to magnetically short them.

2. Apparatus according to claim 1 in which said pairs of magnets are mounted with opposed poles.

References Cited .UNITED STATES PATENTS 3,290,532 12/1966 Lemke et al. 313-77 3,290,533 12/1966 Ammerman 31377 GEORGE HARRIS, Primary Examiner US. Cl. X.R. 3l377 

